Process of producing a smooth continuous surface



8 Claims. (Cl. 204- This invention relates to a method of treatingsurfaces. More specifically it relates to a process for producing levelelectrodeposits having a high degree of smoothness.

As is well known to those skilled in the art, there are numerousoperations which require that the surface of a basis metal be smooth,i.e. must have a reading as measured by a stylus-type instrument of lessthan about 125 microinches, root mean square, and typically a reading of-32 R.M.S. microinches. Such a smooth surface may also be preferablycharacterized by the absence of any discontinuities, including pits,flaws, or irregularities, which may be greater than about three timesthe R.M.S. microinch measurement of the surface.

Typical of the surfaces which must be smooth, i.e. free of imperfectionsof the type noted, may be rolls, drums,

castings, or cylinders which may be used in the manufacture of paper,felt, plastics, food, pharmaceuticals, photographic material, adhesivecompositions, etc. Since the process of this invention may readily beused to treat rolls, reference may for purpose of convenience, behereinafter made to rolls. These surfaces may not functionsatisfactorily unless they are smooth. Furthermore, it is particularlynecessary that this be the case if the surface of the roll is to beelectroplated during manufacture or during rebuilding.

As is well-known, plating with many metals, e.g. chrmium, nickel,cadmium, tin, copper, etc., is particularly characterized by the factthat the deposited plate follows the depressions, i.e. pits,indentations, discontinuities, or other irregularities of the basismetal. Metal surfaces of basis metals, such as cast iron or steel, onwhich a smooth, level metal plate is desired may contain numerous pitsor surface cavities, typically about 0.15 mm. or less in width. Whensuch a basis metal is plated in an electroplating bath, it may be foundthat a continuous smooth plate cannot be formed, and the metal plate mayalso have numerous pits or cavities corresponding to those present inthe basis metal.

To produce smoother electrodeposited surfaces, processes for platingcertain metals, particularly copper and nickel, have been developed inwhich the electrodeposited layer is smoother or more level than is theunderlying layer. Such levelling electroplating processes have beenmoderately successful in plating nickel and copper. They have had littleor no success in plating chromium and other common surface finishes. Theneed for providing smooth and level electrodeposited surfaces is presentin the manufacture of new products, e.g. rolls, as well as in therebuilding of used products wherein the surface has been worn inservice. In these rebuilding operations, the surface is usually regroundand then a new surface is deposited.

It is an object of this invention to provide a process for preparingsmooth and level electrodeposited surfaces. It is a further object ofthis invention to provide a process for preparing a level chromiumelectrodeposited surface. It is still a further object of this inventionto provide a smooth level electrodeposited surface which will serve as abasis metal or underlying layer on which another surface may beelectrodeposited. Other objects will be apparent to those skilled in theart on inspection of the following description.

In accordance with certain of its aspects, this invention United StatesPatent 0 provides a process for producing smooth, continuous metal plateon a basis metal having surface cavities having a width of less thanabout 0.15 mm. which comprises the steps of degassing the basis metal;grit blasting the surface to be plated thereby forming a saturated mattefinish surface; applying to said saturated matte finish surface ahardenable polyester resin; hardening said polyester resin therebyforming a hardened polyester resin coating on said saturated mattefinish surface; grinding the hardened polyester resin coating and thesaturated matte finish surface to a smooth, level surface in whichsubstantially all of the remaining hardened polyester resin is presentin cavities having a width of less than about 0.15 mm. and saidremaining hardened polyester resin constitutes less than 1% of the areaof said smooth, level surface; and electroplating a metal plate oversaid smooth, level surface thereby forming a smooth, continuous metalplate.

Typically the basis metal upon which the smooth, level plate is desiredmay be iron or an alloy thereof, say cast iron or steel, and typicallyit may be an iron or steel roll having pits or cavities which are lessthan 0.15 mm., say 0.02 mm. in Width.

The surface of the roll or other basis metal which is to be plated maypreferably be blasted with fine grit to produce a saturated matte finishin order to provide a surface having good adhesion properties. The gritemployed may be silicon carbide, aluminum oxide, or similar materials,and preferably it may be a No. 40-80 grit. Blasting may be done by meansof an air stream, centrifugal impeller, or other blasting apparatus.Preferably, the surface may be uniformly blasted to a saturated mattefinish, i.e. until further blasting produces no appreciable change inappearance.

The saturated matte finish may, if desired, be produced directly uponthe basis metal. In accordance with certain preferred embodiments ofthis invention, the basis metal may be plated with a thin deposit ofchromium prior to the blasting operation. For example chromium may beplated directly over the basis metal, or a copper-nickel undercoat maybe employed. The chromium deposit may be plated from an acid bathcontaining chromic acid and sulfate ion at a temperature of about 25-50C. and a current density of about 15-50 amperes per square decimeter.Plating may be continued until a deposit of about 0.02-0.1 mm.,preferably 0.05 mm. of chromium is obtained, typically in about 120-200minutes. The so-produced thin chromium deposit may then be lightlyground to remove gross surface imperfections, nodules, etc., andsubjected to the blasting operation hereinbefore described to producethereon a saturated matte finish.

Prior to further treatment, the basis metal may preferably be degassedby heating or other suitable means. Typically, it may be heated to atleast 65 C. and preferably about C. for 3-6, say 4 hours, during whichtime any adsorbed or trapped gases may be liberated. After degassing,the basis metal may be thoroughly cleaned and degassed with carbontetrachloride, benzene, trichloroethylene, tetrachloroethylene or thelike.

After degassing, degreasing, and cleaning, the saturated matte finishmay be coated with a hardenable liquid polyester resin. A hardenablepolyester resin is one which may be cured to form a hard solid curedresin. The hardenable polyester resin employed may contain a saturatedor unsaturated polyester. Saturated polyesters are those prepared fromcompounds containing no ethylenic unsaturation, e.g. phthalic anhydride,isophthalic acid, hexahyd-rophthalic anhydride, adipic acid, succinicacid, etc. together with ethylene, glycol, propylene glycol, butyleneglycol, diethylene glycol, glycerine, etc. Unsaturated polyesters arethose which contain residual ethylenic unsaturation.

They are typically prepared by replacing at least a portion of thesaturated dibasic acid with an unsaturated dibasic acid, such as maleicacid, maleic anhydride, fumaric acid, citranconic acid, mesaconic acid,etc.

The liquid hardenable polyester resins may be hardened or cured byheating, by use of a catalyst, etc. The unsaturated polyesters, whichmay be highly preferred, may be cured by free radical initiators, e.g.methyl ethyl ketone peroxide. Preferably, the unsaturated polyesterresins may contain an ethylenically unsaturated monomer which may assistthe formation of a cured or hardened resin by forming crosslinks.Ethylenically unsaturated monomers are compounds containingpolymerizable carbon-to-carbon double bonds. Typical ethylenicallyunsaturated monomers which may be used to crosslink the unsaturatedpolyesters include styrene, diallyl phthallate, vinyl toluene, triallylcyanurate, acrylic esters, acrylonitrile, etc. Styrene may be apreferred monomer.

Illustrative polyesters which may be employed in the practice of thisinvention may include the following.

Acid

phthallic acid-maleic acid tetrahydrophthallic acid-fumaric acidphthallic acid maleic acid Alcohol ethylene glycol diethylene glycolbutylene glycol propylene glycol The polyester resins may preferably beviscous resins which are liquid at a temperature up to about 40 C. andpreferably at 2540 C. Typical preferred viscous polyester resins includephthallic acid-maleic acid--ethylene glycol polyesters in styrenesolution, preferably containing about 20-40 parts by Weight styrene and6080 parts by weight polyester. Resins of this type are available underseveral trademarks, e.g. Laminac. They are preferably hardened or curedby heating them typically to about 50-100 C. in the presence of afree-radical initiator such as methyl ethyl ketone peroxide and, ifdesired, an accelerator such as cobalt naphthenate.

The hardenable polyester resins may be applied to the saturated mattefinish by troweling, doctoring, spreading, wiping, spraying, etc.Preferably, the polyester may be forced into the depressions of thesaturated matte finish to obtain good bonding. Preferably, the amount applied may be just sufficient to fill all the depressions of thesaturated matte finish, typically about 0.25-0.50, say 0.35 grams ofpolyester per square centimeter of saturated matte finish.

After the polyester resin is applied to the saturated matte finish itmay be hardened, typically by heating to about 50-100 C. say 75 C. forabout 10-60 say 20 minutes. Curing time may be regulated by the amountand type of initiator or catalyst employed. Typically, the articlecoated may be allowed to cool slowly for about 12-24 hours after heatingto ensure complete hardening of the polyester resin.

After the polyester has been hardened, the polyester coating and thesaturated matte surface may be abraded to a smooth level surface.Abrading may be carried out by grinding, sanding or belting. Preferredmeans for abrading may be grinding, typically with a line grit abrasive,say No. 320 to No. 180 grit aluminium oxide, silicon carbide, etc. setin grinding stones. Grinding is preferably continued until substantiallyall of the remaining hardened polyester is present in depressions orcavities having a width of less than about 0.15 mm., say 0.02 mm.Preferably the hardened polyster will constitute less than 1% of thesurface area of the smooth level surface and metal will constitute atleast 99%, say

99.9%, of said surface area. polished to a high luster.

Following the grinding operation, the smooth level surface may becovered with the desired metal plate, typically by electrodepositing themetal plate from a plating bath. The metal plate which is deposited maybe nickel, copper, chromium, etc. Preferably it may be chromium.Typically, chromium may be deposited on the smooth level surface byimmersion of the piece, as cathode, in a chromic acid plating bathcontaining chromic acid, say 250 g./l., and sulfate ion, say 2.5 g./l.at a temperature of about 30-50 C. and a current density of about 1520amperes per square decimeter for about 3 hours. The chromium plateobtained may have a thickness of about 0.07 mm. and may be particularlycharacterized by its smooth, level, continuous surface substantiallyfree from pits, depressions, and discontinuities.

Practice of this novel invention may be observed from the followingillustrative example.

A cast iron roll having dimensions of 150 cm. in length by cm. indiameter was thoroughly cleaned and degreased. Chromium was deposited onthe iron basis metal by electroplating from a bath containing 250 g./ 1.chromic acid and 2.5 g./1. sulfate ion at a temperature of 43-49 C. anda current density of 30 amperes per square decimeter for 90 minutes. Thefinal thickness of the deposit was 0.07 mm. Light grinding was employedto remove nodules and other gross imperfections. The roll was thendegassed by heating to C. for 12 hours. It was blasted while warm withNo. 240 grit aluminum oxide to a saturated matte finish.

While still warm (about 40 C.) the saturated matte finish was coatedwith a hardenable polyester resin containing 60% polyester prepared fromphthalic acid, maleic acid and propylene glycol together with 40%styrene, 0.5% methyl ethyl ketone peroxide as catalyst and 4% cobaltnapthenate as promoter. The polyester resin employed is sold under thetrademark Boatex No. 10. Application was made by pouring on the resinand smoothing and pressing it with a wide spatula. Application wassufiicient to fill all of the depressions of the saturated matte surfaceand to form a thin unifrom coating over the roll. This was about 0.3grams per square centimeter of roll surface. The coated roll was heatedto 75 C. for 20 minutes and allowed to cool slowly over about 12 hoursthereby hardening the polyester resin. When the resin had fullyhardened, the surface of the roll was ground to a smooth level finishwith No. 240 grit The surface may then be grinding stones and a waterlubricant. During grinding,

the surface was periodically washed with clear water. Grinding wascontinued until substantially all of the hardened polyester whichremained was present in cavities having a width of less than 0.15 mm.(about 0.05 average) and the smooth, level surface was about 1% by areapolyester and 99% by area chromium.

Chromium was electrodeposited over the smooth, level surface byimmersing the roll, as cathode in a chromium plating solution containing250 g./l. chromic acid, 2.5 g./l. sulfate ion, at a temperature of 49 C.and a current density of 30 amperes per square decimeter for minutes.The chromium deposit obtained had a thickness of .15 mm. and was smooth,level and remarkably free from pits, cavities or the like. The surfacewas uniformly covered having no pits, cavities or other discontinuoussurface defects. Inspection of this example illustrates the novel,desirable and highly unexpected results obtainable through practice ofthis invention.

Although this invention has been illustrated by reference to specificexamples, numerous changes and modifications thereof which clearly fallwithin the scope of the invention will be apparent to those skilled inthe art.

I claim:

1. The process for producing smooth, continuous metal plate on a basismetal having surface cavities less than about 0.15 mm. in width whichcomprises the steps of degassing the basis metal; grit blasting thesurface to be plated thereby forming a saturated matte finish surface;applying to said saturated matte finish surface a hardenable polyesterresin; hardening said polyester resin thereby forming a hardenedpolyester resin coating on said saturated matte finish surface; grindingthe hardened polyester resin coating and the saturated matte finishsurface to a smooth, level surface in which substantially all of theremaining hardened polyester resin is present in cavities having a widthof less than about 0.15 mm. and said remaining hardened polyester resinconstitutes less than 1% of the area of said smooth, level surface; andelectroplating a metal plate over said smooth, level surface therebyforming a smooth, continuous metal plate.

2. The process for producing smooth, continuous metal plate as claimedin claim 1 wherein the hardenable polyester resin is ethylenicallyunsaturated polyester-styrene resin.

3. The process for producing smooth, continuous metal plate as claimedin claim 1 wherein the metal plate electroplated over said smooth,levelsurface is chromium plate.

4. The process for producing smooth, continuous metal plate on a basismetal having surface cavities less than about 0.15 mm. in width whichcomprises the steps of forming on said basis metal a thin chromiumdeposit; degassing the basis metal; grit blasting the surface to beplated thereby forming a saturated matte finish surface; applying tosaid saturated matte finish surface a hardenable polyester resin;hardening said polyester resin thereby forming a hardened polyesterresin coating on said saturated matte finish surface; grinding thehardened polyester resin coating and the saturated matte finish surfaceto a smooth, level surface in which substantially all of the remaininghardened polyester resin is present in cavities having a width of lessthan about 0.15 mm. and said remaining hardened polyester resinconstitutes less than 1% of the area of said smooth, level surface; andelectroplating a metal plate over said smooth, level surface therebyforming a smooth, continuous metal plate.

5. The process for producing smooth, continuous plate as claimed inclaim 4 wherein the thin chromium deposit has a thickness of 0.050.1 mm.

6. The process for producing smooth, continuous plate as claimed inclaim 4 wherein the hardenable polyester resin is an ethylenioallyunsaturated polyester-styrene resin.

7. The process for producing smooth, continuous plate as claimed inclaim 4 wherein the metal plated electroplated over said smooth, levelsurface is chromium plate.

8. The process for producing smooth, continuous chrom-ium metal plate ona basis metal having surface cavities less than about 0.15 mm. in widthwhich comprises the steps of forming on said 'basis metal a chromiumdeposit having a thickness of 0.05-0.1 mm.; degassing the basis metal;grit blasting the surface to be plated thereby forming a saturated mattefinish surface; applying to said saturated matte finish surface ahardenable ethylenically unsaturated polyester-styrene resin in amountsuificient to fill the depressions of said saturated matte finishsurface; heating said hardenable polyester resin to 100 C. therebyhardening said polyester resin and forming a hardened polyester resincoating on said saturated matte finish surface; grinding the hardenedpolyester resin coating and the saturated matter finish surface to asmooth, level surface in which substantially all of the remaininghardened polyester resin is present in cavities having a width of lessthan about 0.15 mm. and said remaining hardened polyester resinconstitutes less than 1% of the area of said smooth, level surface; andelectroplating a chromium metal plate over said smooth, level surfacethereby forming a smooth, continous chromium metal plate.

References Cited by the Examiner FOREIGN PATENTS 216,710 8/1958Australia. 566,776 1/ 1945 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner. VAN SISE, Assistant Examiner.

1. THE PROCESS FOR PRODUCING SMOOTH, CONTINUOUS METAL PLATE ON A BASISMETAL HAVING SURFACE CAVITIES LESS THAN ABOUT 0.15 IN WIDTH WHICHCOMPRISES THE STEPS OF DEGASSING THE BASIS METAL; GRIT BLASTING THESURFACE TO BE PLATED THEREBY FORMING A SATURATED MATTE FINISH SURFACE;APPLYING TO SAID SATURATED MATTE FINISH SURFACE A HARDENABLE POLYESTERRESIN; HARDENING SAID POLYESTER RESIN THEREBY FORMING A HARDENEDPOLYESTER RESIN COATING ON SAID SATURATED MATTE FINISH SURFACE; GRINDINGTHE HARDENED POLYESTER RESIN COATING AND THE SATURATED MATTE FINISHSURFACE TO A SMOOTH, LEVEL SURFACE IN WHICH SUBSTANTIALLY ALL OF THEREMAINING HARDENED POLYESTER RESIN IS PRESENT IN CAVITIES HAVING A WIDTHOF LESS THAN ABOUT 0.15 MM. AND SAID REMAINING HARDENED POLYESTER RESINCONSTITUTES LESS THAN 1% OF THE AREA OF SAID SMOOTH, LEVEL SURFACE; ANDELECTROPLATING A METAL PLATE OVER SAID SMOOTH, LEVEL SURFACE THEREBYFORMING A SMOOTH, CONTINUOUS METAL PLATE.